Negative electrode active material for nonaqueous electrolyte secondary batteries and nonaqueous electrolyte secondary battery containing negative electrode active material

Abstract

In a nonaqueous electrolyte secondary battery in which SiO x is used as a negative electrode active material, initial charge/discharge efficiency and cycle characteristics are improved. Provided is a negative electrode active material, containing particles made of SiO x (0.5≦X≦1.5), for nonaqueous electrolyte secondary batteries. In the negative electrode active material, amorphous carbon is stuck on carbon coatings. The particles made of SiO x preferably have a size of 1 μm to 15 μm. Particles of amorphous carbon preferably have a size of 0.01 μm to 1 μm. One hundred percent of the surface of SiO x is preferably covered by the carbon coatings.

1 . A negative electrode active material for nonaqueous electrolyte secondary batteries being a particulate negative electrode active material used in nonaqueous electrolyte secondary batteries, the negative electrode active material comprising:
 mother particles made of SiO x  (0.5≦X≦1.5);   carbon coating layers each covering at least one portion of the surface of a corresponding one of the mother particles; and   amorphous carbon particles stuck on the carbon coating layers.   
     
     
         2 . The negative electrode active material for nonaqueous electrolyte secondary batteries according to  claim 1 , wherein the mother particles have an average size of 1 μm to 15 μm and the amorphous carbon particles have an average size of 0.01 μm to 1 μm. 
     
     
         3 . The negative electrode active material for nonaqueous electrolyte secondary batteries according to  claim 1 , wherein 100% of the surface of each of the mother particles is covered by a corresponding one of the carbon coating layers. 
     
     
         4 . A nonaqueous electrolyte secondary battery comprising:
 a negative electrode containing the negative electrode active material according to  claim 1 ;   a positive electrode containing a positive electrode active material;   a separator placed between the positive electrode and the negative electrode; and a nonaqueous electrolyte.